The global demand for power continues to increase. Often, the combustion or burning of fossil fuels produces power to meet this demand. These processes are thermochemical in nature and often result in unburned fuel, particulates, and other noxious chemicals being injected into the atmosphere. For example, coal is burned to produce thermal energy to heat water. The resulting steam drives large turbines coupled to generators to thereby produce electricity. In the absence of downstream environmental controls, such as, scrubbers, coal burning power plants can introduce undesirable gases, residual pollutants, and particulates into the air. By way of additional example, an internal combustion engine in an automobile is configured to combust gasoline to drive a crankshaft that ultimately propels the automobile. Similarly, if not for downstream environmental controls, unburned fuel and incomplete combustion products often pollute the air. As the demand for power increases, the environmental impact of these methods of producing power is becoming more acute. For instance, it is now thought that waste gases from coal burning power plants are linked to global warming.
Driven by a desire to reduce direct environmental pollution, alternative sources of power are being investigated. One of the more promising sources of clean power is a fuel cell. Generally, a fuel cell produces electrical power from an electrochemical process, rather than a thermochemical process, and depending on the fuel used, may generate electrical power without the pollution associated with combustion or burning of fossil fuels.
One example of such a fuel cell is the Proton Exchange Membrane (PEM) fuel cell. A PEM fuel cell produces electrical power by an electrochemical process that includes a fuel, such as hydrogen gas, and an oxidant, such as oxygen gas. Hydrogen and oxygen are combined by an electrochemical process that produces electricity while emitting only water and heat to the environment. Thus, a PEM fuel cell utilizing hydrogen as a fuel and air (i.e., the source of oxygen) is essentially a zero emission system.
Fuel cells, such as the PEM fuel cell, are, however, not without their operational difficulties. For example, the Oxygen Reduction Reaction (ORR) at the cathode of a PEM fuel cell is often slow and is generally the largest source of inefficiency in a PEM fuel cell. Because oxygen in air is predominately diatomic (O2), the molecule must be broken before oxygen can participate in the electrochemical reaction. The slow kinetics associated with the ORR are thought to be due to the oxygen-oxygen pi-bond being relatively strong and thus difficult to break. To address this difficulty, commercially viable PEM fuel cells include significant amounts of platinum in the cathode. The platinum significantly improves the ORR kinetics by facilitating breaking of the pi-bond in O2. So, on the one hand, the presence of the platinum improves the otherwise slow kinetics for ORR and makes electrical power generation with PEM fuel cells a commercial possibility. On the other hand, however, inclusion of platinum increases the capital costs associated with PEM fuel cells and thus, from a cost perspective, inhibits large scale introduction of these devices.
Consequently, there is a need for cost-effective catalyst materials, electrodes, and for devices using those cost-effective catalyst materials.